1. Field of the Invention
The present invention relates to a method of injection molding a closure with a continuous internal rigid rib, an injection molded container closure with an internal lead-in structure and a mold for forming the same.
2. Brief Description of the Prior Art
The prior art discloses a wide variety of threaded container closures with additional internal structures. One typical internal structure for a threaded container closure is the interference elements for a tamper-evident band. The interference elements are intended to engage the container after the container closure is attached to the container to prevent the tamper-evident band from subsequently being removed from the container. This interference results in the separation of the tamper-evident band from the container closure when the container closure is removed from the container after initial attachment. This separation is intended to evidence any subsequent opening of the container to provide the desired tamper evidence to the user. The interference elements must allow the container closure to be initially attached onto the container without separating the tamper-evident band from the container closure at that point while subsequently acting to prevent the removal of the tamper-evident band prompting separation from the container closure as discussed above.
The interference elements can take several different shapes. An upward extending (i.e., extending toward the closed end of the container closure) integral continuous barb can be considered as the most effective shape for an interference element, but this shape is relatively difficult to efficiently manufacture. One solution addressing the manufacturing problem is to form the barb as a downwardly extending member as molded, which is folded up following the molding process. This solution is found in U.S. Pat. Nos. 4,848,614; 5,090,788; 4,807,771; 4,546,892; 4,595,110; 5,725,115; 5,775,527; 5,913,437; 6,116,442; and 6,119,883. Another known shape for the interference element is a shallow bead since the shallow bead presents less problems in manufacturing, but is not optimal for providing the amount of interference needed. See U.S. Pat. Nos. 4,549,667; 4,526,282; and 4,878,589. Another shape for the interference element is to form the element as a series of spaced separate elements to avoid a continuous hoop structure. See U.S. Pat. Nos. 4,196,818; 5,487,481; 6,112,923; 6,089,390; 6,068,151; 5,992,661; 5,950,850; 5,547,092; 5,064,084; 4,828,127; 4,497,765; 4,511,054; 4,520,939; 4,674,643; 5,328,044; 6,213,321; and 5,050,753.
Within the meaning of this specification, there is a distinction between a continuous projection or barb formed as a rib and a continuous projection or barb formed as a bead. This distinction between a bead and a rib within the meaning of this specification relates to the relative shape of the respective structure. In a projection of generally rectangular cross-section, a rib is a structure having a length-to-width ratio of at least one and one-half. A bead will have a length-to-width ratio less than one and one-half. The length of a projection is measured along the direction in which the projection is extending away from the side wall of the container closure. In non-rectangular shapes, the width would be the average width of the projection. Another term requiring further clarification within this specification is continuous. A continuous projection is a projection extending about three hundred sixty degrees around the side wall of the container closure such that the projection maintains hoop-like characteristics. A continuous projection need not actually form a complete closed ring. It is the hoop like characteristics that are important. The hoop like characteristics raise the issues associated with removing the threaded container closure from the mold in an efficient and cost-effective manner.
There is a need in the prior art to form a threaded, closed end container closure with a continuous internal rib on the container side wall that can be efficiently manufactured. The internal rib could be effectively used as an interference element for a tamper-evident band. Other uses for such an internal continuous rib are also possible. It is the object of the present invention to overcome the drawbacks of the above-described prior art. It is a further object of the present invention to provide a container closure with an internal continuous rib for use as an interfering element for a tamper-evident band and which improves the initial attachment of the container closure onto the container.